Electronic flash inhibit arrangement

ABSTRACT

Electronic flash apparatus for a camera having automatic focusing with sonic ranging has a charge control system which inhibits charging of the flash tube capacitor during at least the automatic focusing operation of the camera. The flash apparatus thus schedules capacitor charging to occur at times other than the sonic ranging for automatic focusing, and thereby avoids the likelihood that spurious radiation from the capacitor-charging oscillator interferes with the sonic ranging operation.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This invention relates to U.S. Pat. application Ser. No. 889,251 for"Control System for Flash-Illuminated Automatic Focusing Camera", by G.Harrison, filed Mar. 23, 1978 in common assignment herewith.

BACKGROUND OF THE INVENTION

This invention relates to electrical apparatus for powering automaticcamera equipment in a manner to avoid interference between cameraoperations. More particularly, the invention provides electrical controlapparatus which limits the charging of a photographic flash capacitor toselected operating conditions when other interference-sensitive elementsof the camera system are quiescent. The invention is described withparticular reference to an electronic flash unit having control meanswhich inhibits the charging operation when a sonic ranging device forautomatic camera focusing is active.

Electronic flash units for photography are well known. The unitsconventionally have a battery-powered oscillator for producingalternating voltage which is rectified to charge a flash-poweringstorage capacitor. It is also known to control this capacitor-chargingoperation due to restrictions on the available battery power. The priorart on this subject includes U.S. Pat. Nos. 3,846,812; 4,001,639 and4,064,519.

The advent of automatic focusing for cameras by sonic ranging raises theproblem of a focusing malfunction due to interference with radiationfrom the flash unit. The focusing system emits sonic energy andpositions the objective lens of the camera in response to reflectionssensed from the object to be photographed. However, faulty ranging canoccur when the focusing system picks up stray radiation from thecapacitor-charging oscillator of the flash unit. The result of suchfaulty ranging operation is improper focusing of the objective lens ofthe camera and consequently an improperly focused photograph. It isunderstood that the interfering radiation is electromagnetic in nature.

The use of shielding to contain electromagnetic radiation from theflash-unit oscillator, and the use of selected frequency ranges for theranging system and for the oscillator can diminish the interferenceproblem, but recourse to these solutions tends to be costly. Moreover,the complete isolation of the ranging system from the capacitor-chargingoscillator with either technique, so that the likelihood of a rangingmalfunction is rendered negligible, is elusive to attain.

The prior art regarding automatic camera focusing includes U.S. Pat. No.3,522,764, and commonly-assigned pending U.S. Pat. applications Ser.Nos. 729,289 for "Automatic Focusing Camera" by E. Shenk and Ser. No.729,392 for "Ultrasonic Ranging System For Camera" by J. Muggli.

It is an object of this invention to provide apparatus for controllingphotographic electronic flash equipment to operate without interferencewith sonic ranging for automatic camera focusing. To this end it is anobject of the invention to provide photographic electronic flashequipment which responds to electrical signals available from anautomatic sonic-focusing camera for controlling the capacitor-chargingoscillator for operation without electromagnetic interference with thecamera focusing operation. It is a further object of the invention toprovide flash equipment-controlling apparatus of the above characterwhich requires few components, and is otherwise comparatively low incost.

A specific object of the invention is to provide a regulatedphotographic electronic flash unit incorporating control apparatus foroperation without interfering with automatic camera focusing.

It is also an object of the invention to provide apparatus of the abovecharacter which operates with a minimum of operator attention orconcern.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

GENERAL DESCRIPTION

An electronic photographic flash unit embodying the invention hascontrol elements which inhibit the flash unit oscillator from chargingthe storage capacitor during selected intervals of camera operation,including at least automatic focusing. The oscillator is thus quiescent,and emits no potentially-interfering radiation, either electrical orsonic, during the automatic focusing of the camera. Thestorage-capacitor in the flash unit normally is charged to the properoperating level prior to the start of the camera operating cycle, andretains sufficient charge during the inhibit interval to produce properflash illumination.

The flash unit can inhibit the charging oscillator in response tosignals available from the camera. This is particularly convenient wherethe camera operates with a cycle which is sufficiently automatic toproduce a succession of control signals as the operating cycle proceeds.Alternatively, the flash unit can include a timer which initiates theinhibit interval in response to a single camera-signal and automaticallyterminates it at a later time. With the latter embodiment, the intervalof the inhibit timer is sufficiently long to allow completion of atleast the automatic focusing operation of the camera. Thereafter, in theabsence of other constraints, the flash unit can be released to resumecapacitor-charging operation, thereby to ensure that the storagecapacitor is fully charged at the instant the camera sends the flashfire signal to the flash unit.

The invention accordingly comprises the features of construction,combinations of elements, and arrangements of parts exemplified in theconstructions set forth below, and the claims indicate the scope of theinvention.

DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the invention,reference should be made to the following detailed description and theaccompanying drawings, in which:

FIG. 1 shows in schematic form a camera with which the invention isused;

FIG. 2 is a block schematic diagram of a charge control system accordingto the invention;

FIG. 3 is a more detailed schematic diagram of the charge control systemof FIG. 2; and

FIG. 4 is a partial schematic diagram of another charge control systemaccording to the invention.

DESCRIPTION OF ILLUSTRATED EMBODIMENTS

A camera 10 equipped with a charge control system in accordance with theinvention has, as FIG. 1 diagrammatically shows, a film and battery pack12 which presents one film unit therein at the image plane and inoptical alignment with a mirror reflector 14 and a lens system 16. Thelens system includes a variable focus objective lens. An exposurecontrol system 18, including a shutter mechanism, is in opticalalignment behind the lens system 16. A film transport mechanism,including a pair of spread rolls 20 and a transport motor 22, isarranged to transport an exposed film unit from the film pack 12 anddraw it through the spread rolls before discharging it from the camera10. The camera 10 also has an automatic focusing system 24 with afocusing motor 24a coupled to selectively focus the lens system 16. Acamera logic unit 26 schedules the camera operations under power fromthe battery in the pack 12 when initiated by the shutter button 30. Thecamera also has a viewer 28.

The camera 10 is equipped with an electronic flash unit 32, which alsooperates in conjunction with the logic unit 26. The illustrated flashunit 32 has a regulated charge system and produces a fixed, knownquantity of light, and the illustrated camera 10 adjusts the exposurecontrol system 18 for proper film exposure in accordance with thedistance to the object being photographed as provided by the automaticranging elements of the focus system 24. The illustrated camera thusexposes film with a non-automatic strobe or flash unit using a so-calledfollow-focus exposure control system.

In a camera 10 where the viewer 28 is a simple viewfinder, the operatorcan view the subject to be photographed independent of the focuscondition of the camera. Thus, when the operator has the scene to bephotographed properly in view, s/he depresses the shutter button toinitiate a camera operating cycle, controlled by the logic unit 26 andthe flash unit 32, in which the camera automatically focuses on thesubject in the center of the viewfinder, exposes a film unit with flashillumination, and transports the exposed film unit from the film packthrough the rollers and discharges it from the camera. Aside from theautomatic focusing system 24 and the flash unit 32, the structure andoperation of the camera 10 where the viewer 28 is a simple viewfindercan be the same as found in a commercially available PRONTO! brandcamera marketed by the Polaroid Corporation. Accordingly, these elementsof the camera 10 are not described further.

The automatic focusing system 24 can be constructed as described in theabove-noted U.S. Pat. No. 3,522,764 and U.S. Pat. applications Ser. Nos.729,289 and 729,392. As the noted patent describes, it emits sonicenergy with an ultrasonic frequency, and senses reflections from thecenter of the camera field of view. Electrical circuits develop aranging signal in response to the sensed sonic energy and drive thefocusing motor to focus the lens systems on the object that reflectedthe sonic energy. Such a system, however, can be subject to interferencefrom the stray radiation which a flash-unit oscillator typicallyproduces. When this occurs, the system develops a faulty ranging signal,and consequently the camera lens is focused at an incorrect imagedistance. The flash unit 32 which the invention provides, however, isquiescent during the automatic focusing, and hence the camera system ofFIG. 1 is free of this problem.

FIGS. 2 and 3 show a flash unit 32 connected with a viewfinder camera 10operating in the foregoing manner. As shown schematically in FIG. 2, theflash unit 32 is activated with a normally-open on-off switch 34 thatcloses to energize a power oscillator and converter 38 from a flashbattery 36. The power converter 38 develops a high direct voltage whichit applies to an energy storage capacitor 40 connected in parallel witha flash tube 42. The charge control system also has a comparator 44 thatcompares a known portion of the voltage across the storage capacitor 40with a reference voltage. A normally-inactive regulator driver 46responds to the signal the comparator produces when the storagecapacitor voltage attains a desired level to activate an oscillatorcontrol circuit 48. The control circuit 48 is normally inactive, butwhen activated by the regulator driver 46, it disables the oscillator ofthe power converter 38. The converter then stops charging the capacitor40. Moreover, the flash unit produces no stray radiation, eitherelectromagnetic or sonic, when the oscillator is disabled.

A trigger circuit 50 responds to a flash pulse from the camera, appliedthrough an interface circuit 52, to initiate conduction in the flashtube 42. The flash tube then dissipates the charge stored in capacitor40 and produces a bright flash of illumination for the camera.

The oscillator control circuit 48 is also activated to switch off thepower converter 38 by an assertive signal from an OR gate 54, which isconnected to switches within the camera 10 logic unit 26.

FIG. 2 also shows that the flash unit 32 plugs by way of a connector 56onto the camera 10. The connector 56 interconnects the flash unit withthe camera logic unit 26 for applying, by way of conductors 58a and 58b,the flash pulse from the camera logic unit to the trigger circuit 50, byway of the interface circuit 52. In the illustrated embodiment, a cameraswitch S3 applies one side of the battery 12a to the conductor 58b foran interval that includes the camera exposure time. The camera logicunit switches the conductor 58a to the other side of the camera batteryat the proper time to produce the flash illumination synchronized withfilm exposure. The illustrated arrangement also includes a conductivejumper 60 within the flash unit which, by way of the connector 56,connects one side of the camera battery 12a to the camera logic unit 26via a conductor 62, thereby signalling the logic unit that the flashunit is plugged onto the camera.

The illustrated camera also has two other switches S1 and S2 which applysignals, by way of connector 56, to the flash unit. The signals areapplied to the OR circuit 54 to inhibit operation of the poweroscillator and converter 38 and thereby to preclude electricalinterference with the camera automatic focus system 24 during selectedportions of the camera operating cycle. The net effect of the twoswitches S1 and S2 is to ensure that the OR circuit 54 receives at leastone assertive signal throughout at least the automatic focusingoperation of the camera cycle. The OR circuit in response disables thecapacitor-charging power oscillator during this camera operation. Moreparticularly, in the illustrated embodiment, switch S1 closes upondepression of the shutter button 30 and remains closed only as long asthe operator depresses the shutter button. The switch S2 applies anassertive signal to the flash unit 32 during operation of the camerafocus mechanism 24. The switch S2 automatically closes, after theshutter button is depressed, in response to the camera lens system beingmoved from the rest position and remains closed until the automaticfocus mechanism returns the lens system 16 to the rest position. (Thelens system 16 is only in the rest position when the camera is not in anoperating condition; that is, no pictures are taken with the lens in therest position.)

The operation of the elements described in FIG. 2 commences when theuser turns on the flash unit 32 by closing switch 34, which is normallyopen. The closed switch 34 applies the battery 36 voltage to the poweroscillator and converter 38, which commences charging the storagecapacitor 40. When the comparator 44 signals that the voltage across thestorage capacitor 40 has attained the desired level, the regulatordriver 46 activates the oscillator control circuit 48 to terminatefurther operation of the power converter 38.

While the operator maintains the on/off switch 34 closed, but does notdepress the camera shutter button 30, the capacitor 40 charge begins todissipate from the selected level. When it drops to a lower thresholdlevel, the comparator 44 no longer activates the regulator driver, andthe control circuit becomes inactive. The power converter 38 thenresumes operation and recharges the storage capacitor quickly to thedesired level, at which point it is again disabled by the comparator 44,the driver 46 and the control circuit 48. The power converter 38,comparator 44, driver 46, and control circuit 48 thus operate as adiscretely regulated d.c. to d.c. power converter, and maintain thecapacitor, once it is charged, within a selected voltage of the desiredcharge level. The regulation operates with discrete on and offconditions.

When the user presses the shutter button 30 while the flash unit switch34 is closed, the resultant closures of switches S1 and S2 activate thecontrol circuit 48 to disable the power oscillator and converter. Withthe oscillator thus turned off, the flash unit produces no significantradiation that can interfere with the focus system of the camera. SwitchS3 is also closed in response to pressing the shutter button 30. Afterclosure of at least switch S1, the camera activates the sonic focusingsystem 24, FIG. 1, and then produces the flash fire signal whileoperating the exposure unit 18. The trigger circuit responds to theflash signal to fire the flash tube from the charged capacitor 40 duringthe film exposure. The illustrated camera control unit 26 then activatesthe transport motor 20, and finally resets the automatic focus system24. These latter actions open switches S2 and S3. When the user also hasreleased the shutter button so that switch S1 opens, the flash unit willagain charge the capacitor 40 in preparation for another exposure.Release of the flash unit switch 34, however, terminates all chargingoperation.

FIG. 3 shows a preferred flash unit circuit for the charge controlsystem of FIG. 2. The on-off switch 34 applies the battery 36 voltage tothe converter 38, which employs a transistor 70 with theemitter-collector path in series with the primary winding 72a of astep-up transformer 72. The transformer has a feedback winding 72bbetween the transistor base and a voltage divider formed by fixedresistors 74 and 76. The series combination of a capacitor 78 andresistor 80 is connected between the positive battery voltage and theinterconnection of the feedback winding with the voltage dividerresistors. The circuit develops a stepped-up alternating voltage acrossthe transformer 72 secondary winding 72c, across which a capacitor 82 isconnected, and a diode 84 rectifies this output voltage to develop theconverter 38 output direct voltage.

The energy storage capacitor 40 receives the high direct voltage outputfrom the converter 38 and applies it across the terminals of the cameraflash tube 42. This power converter 38 is similar to that described inU.S. Pat. No. 4,068,151, to which reference should be had for furtherdetails. A capacitor 86 is connected between the positive battery line36a and the return path 36b in the flash unit to increase the chargesystem efficiency by supplying peak currents for the power converter 38.It also suppresses electronic noise.

The illustrated comparator 44 (FIG. 2) is constructed with a seriescombination of fixed resistor 88, potentiometer 90, and fixed resistor92 forming a voltage divider in parallel with the energy storagecapacitor 40. The potentiometer tap applies a known portion of thevoltage across the capacitor 40 to the cathode of a zener diode 94, theanode of which is connected to the base of a transistor 96. A capacitor98 is connected between the transistor collector and the zener cathode,and a resistor 100 is connected between the base and the d.c. return orground path, to which the transistor emitter is connected. U.S. Pat. No.4,068,151 for "Regulated Strobe with Hysteresis" describes the operationof this comparator 44 construction.

The signal which the comparator transistor 96 develops at the collector,which is the comparator 44 output signal, is applied through a seriesresistor 102 to the base of a transistor 104. A resistor 106 isconnected between the transistor base and the positive battery voltage.The emitter is connected to the positive battery line 36a, and thetransistor collector is connected through a resistor 108 to the base ofa transistor 110. A resistor 112 is connected between the transistor 110base and the return path. The transistors 104 and associated resistorsconstitute the regulator driver 46 of FIG. 2.

With further reference to FIG. 3, the OR circuit 54 of FIG. 2 employstwo logic diodes 114 and 116 connected respectively to apply the signalsfrom switches S1 and S2 to the base of a transistor 120 throughcurrent-limiting resistor 122. A resistor 118 is connected between thetransistor base and the flash unit return conductor. Transistor 120 anda further transistor 124 constitute the FIG. 2 control circuit 48. Aresistor 126 and isolating diode 128 couple the collector of transistor120 to the base of transistor 124. The transistor 124 emitter isconnected to the battery line 36a, and a resistor 130 is between thebase and that line. The emitter-collector path of transistor 124 is thusin parallel with the emitter-base junction of the oscillator andconverter transistor 70, such that when the transistor 124 is conductingit in effect shunts the converter transistor 70.

The base of transistor 124 is direct-coupled through resistor 132 to thecollector of transistor 110. A flash-ready indicator is also provided bya light-emitting diode 134 and series limiting resistor 136 in parallelwith resistor 132.

The interface circuit 52 of FIG. 2 enables the flash unit 32 to beconnected for operation with circuits of the camera 10. The illustratedinterface construction shown in FIG. 3 employs a transistor 138 with theemitter connected to the connector terminal 56c. The switch 140 ispreferably operated with the flash unit on-off switch to present a highimpedance to the camera at terminal 56f when the flash unit is OFF. Thetransistor base is connected to the interconnection of resistors 142 and144 and the resistor 144 is connected in series with the switch 140 tothe connector terminal 56f that receives the flash fire signal. Aresistor 146 is in parallel with the two resistors 142 and 144.

The flash-initiating signal which transistor 138 develops at thecollector is applied through a series resistor 148 and across a shuntcapacitor 150 and resistor 151 to the gate of a silicon controlledrectifier 152. The SCR 152 is arranged with the capacitor 150 andresistor 151 in a conventional trigger stage, with the cathode connectedto the return line. The SCR anode is connected to the interconnection ofa voltage divider formed with resistors 154 and 156 and which is inparallel with the energy storage capacitor 40, and is connected througha series coupling capacitor 158 to the primary winding of a triggertransformer 160. The transformer 160 secondary winding is connected tothe trigger electrode of the flash tube 42.

The circuit of FIG. 3 converts the relatively low, for example six volt,voltage of the flash unit battery 36 to a significantly higher d.c.voltage, for example having a value in excess of three hundred volts,which it applies across the energy storage capacitor 40. During theinitial charging operation all transistors other than the poweroscillator and converter transistor 70 are nonconducting. When thevoltage across the storage capacitor 40 attains the desired maximumlevel and zener diode 94 conducts, transistor 96 begins conducting. Theresultant voltage drop at the collector of that transistor biasestransistor 104 ON. The emitter-base conduction in transistor 104switches transistor 110 ON, which in turn switches transistor 124 ON.The resultant low emitter-collector impedance of transistor 124 ineffect short circuits the oscillator transistor 70 to terminate furtheroperation of the converter. The charging of the storage capacitor 40hence stops at the level which initiated transistor 96 conduction. Whenthe discharge of capacitor 98 in the comparator 44 and the discharge ofthe main energy storage capacitor 40 cause the comparator transistor 96to decrease in conduction, transistor 124 is switched to thenon-conductive state through transistors 104 and 110, thereby releasingthe power converter to recharge the storage capacitor 40 to thespecified level. The power converter now operates in a regulating mode,repetitively switching ON and OFF to maintain the desired charge acrossthe storage capacitor 40.

When the camera control unit 26 applies a flash pulse to connectorterminal 56f, conduction through resistor 146 in the interface circuit52 develops a voltage drop across the voltage divider resistors 142 and144 and hence biases transistor 138 to conduction. The resultant pulseon the transistor collector, which is referenced to the camera batteryground through connector terminal 56d, initiates conduction in the SCR152. The trigger circuit then initiates photograph-illuminating flashconduction with the energy stored in capacitor 40.

The camera logic unit 26 produces the flash pulse only when the userdepresses the shutter button 30 which, as described, results in theclosure of the camera switches S1, S2 and S3. Closure of switches S1 andS2 biases diodes 114 and 116, respectively, of the OR circuit 54 toconduct, which biases transistor 120 to conduct. This turns ONtransistor 124, which turns off transistor 70 so that the capacitorcharging operation halts. The oscillator and converter 38 therebyremains inactive during the ensuing automatic ranging and focusingoperation. In the illustrated embodiment of FIGS. 2 and 3, where cameraswitch S2 remains closed until the camera lens returns to the at-restposition at the end of the camera cycle, the flash unit charge systemremains disabled for the same interval. With most cameras, especiallycameras other than of the single reflex type, this interval is so shortthat the storage capacitor readily retains sufficient charge to provideample power for the flash illumination.

The charge control system of FIGS. 2 and 3 thus charges the energystorage capacitor to a selected level and regulates the capacitor chargeat that level. The system responds to a camera flash pulse to fire theflash tube from the charged storage capacitor. However, the systemdisables the power oscillator and converter throughout at least thecamera cycle step of automatic ranging and focusing. That operationconsequently proceeds without interference from any electromagnetic orsonic radiation from the oscillating operation of the flash unitconverter 38.

The invention can also be practiced by inhibiting the flash unitoscillator only during the automatic ranging step of camera operation,and hence allow flash unit charging during subsequent camera operations.This sequence can be particularly useful with an automatically-focusingSLR camera such as the Polaroid Corporation Sonar SX-70 One Step Camera.With such a camera, the image the user sees is in focus only when thecamera objective lens is focused. Hence the user needs a brief interval,usually measured in fractions of a second, between the automaticfocusing operation and the exposure operation in which to frame andpreview the scene to be photographed. Resumption of flash chargingimmediately after the automatic focusing is hence desirable to ensurethat the flash capacitor is fully charged at the post-previewing timewhen exposure takes place. The resumption of flash unit-charging afterautofocusing can be done, for example, with the arrangement of FIGS. 2and 3 simply by actuating the flash unit OR circuit 54 only during thebrief interval of automatic ranging.

Alternatively, the flash unit can employ a timing circuit to limit theinhibit duration, and FIG. 4 shows such a timing circuit. (Elements ofFIG. 4 which corresponds to elements of any prior figure bear the samereference numeral with a superscript prime.) The timing circuit of FIG.4 is connected to charge control system of the FIG. 3 flash unit 32 atthe FIG. 3 terminal 56a, 56b and 56d and at the connection points 4a and4b. It hence replaces the the FIG. 3 elements 114, 116, 118, 120, 122,126 and 128.

In place of these elements, the timing circuit has diodes 114' and 116'connected to the terminals 56a' and 56b', and employs two transistors162 and 164. The collector of transistor 164 is connected throughlimiting resistor 126' and isolating diode 128' to connection point 4a'.The base of that transistor is connected directly to the collector oftransistor 162, and a resistor 166 is connected between the base and theinterconnected cathodes of diodes 114' and 116'. A resistor 168 isconnected between the transistor 162 emitter and the return pathprovided at terminal 56d' and point 4b'. A resistor 170 is connectedbetween the diode cathodes and transistor 162 base, and a timingcapacitor 172 is connected from the base to the return conductor.

The diodes 114' and 116', like the corresponding diodes in FIG. 3,supply operating power to the flash-unit transistor to which theyconnect. Hence, in the absence of camera voltage at either terminal 56a'or 56b', both transistors 162 and 164 are nonconducting and capacitor172 is discharged. However, upon closure of camera switch S1, diode 114'applies the power from the camera battery to both transistors, andtransistor 164 becomes conductive. The current path through thecollector emitter junction drives the FIG. 3 transistor 124 toconduction, which disables the oscillator transistor 70. The initiallydischarged capacitor 172, however, holds transistor 162 non-conductivefor a timing interval determined by resistor 170 and the capacitor. Whenthe capacitor voltage charges through resistor 170 to the point where itexceeds the reference voltage across resistor 168 sufficiently to switchtransistor 162 ON, the drop in collector voltage at the lattertransistor drives transistor 164 OFF. The FIG. 3 transistor 124 thenceases conduction and transistor 70 resumes capacitor-chargingoperation.

Transistor 162 continues conducting, thereby biasing transistor 164 OFF,so long as any one of the camera switches S1 and S2 is closed to applypower from the camera battery. In this manner, the timing circuit ofFIG. 4, with very few additional components, provides an electronicflash unit which is disabled only during the very brief interval ofautomatic camera ranging.

The invention thus provides an electronic flash unit for asonically-ranging auto-focus camera. The flash units responds to one ormore signals available from the camera to inhibit flash-chargingoscillator elements that are potential sources of interference with thesonic ranging operation of the auto-focus system. The flash unit remainsfully active until disabled in response to camera signals that mark thestart of the auto-focus operation. In one embodiment the flash unitthereafter remains disabled from charging the flash-powering capacitoruntil the camera signals terminate. A second embodiment provides aseparate inhibit timer that releases the flash unit from the inhibitmode after a selected interval. With both embodiments, the inhibitoperation does not detract from the charge on the flash unit capacitor,so that it remains sufficient for full flash illumination for asignificant interval after the onset of the inhibit.

The flash unit which the invention provides thus leaves the camera withwhich it is used free for accurate automatic sonic ranging and focusingwithout the potential of interference from the flash unit.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings be interpreted as illustrative and not in a limiting sense. Asone example, although illustrated with a flash unit having a batteryseparate from the camera battery, a flash unit embodying the inventioncan be powered from the camera battery. As a further example, theinvention can be practiced by those skilled in the art with a flash unithaving a non-regulated charge control system.

Further, the following claims are intended to cover all of the genericand specific features of the invention herein described, and allstatements of the scope of the invention which as a matter of languagemight be said to fall therebetween.

Having described the invention, what is claimed as new and secured byLetters Patent is:
 1. Electronic flash apparatus for use with a cameraof the type having a variable focus objective lens and having automaticfocusing means with ranging means for the automatic focusing of theobjective lens, electrically-energizable camera control means responsiveto manual actuation for automatically operating the ranging means fordriving the objective lens to a focus position with respect to a sceneto be photographed, and means for providing a camera signal commencingin response to the manual actuation of the control means and not laterthan the automatic focusing operation, and wherein the camera focusingmeans is subject to detrimental interference from spuriouselectromagnetic radiation,said electronic flash apparatus havinganenergy-storage capacitor and a flash-discharge tube, charging meansenergizable by an applied supply voltage for producing an alternatingvoltage and a direct voltage in response thereto, and for charging thecapacitor with the direct voltage, means responsive to a flash firesignal from the camera for discharging the capacitor through the flashtube, and further comprisingcontrol means responsive to said camerasignal for disabling said charging means from producing said alternatingvoltage, so that the flash apparatus is disabled from producing spuriouselectromagnetic radiation, during at least the operation of the camerafocusing means.
 2. Electronic flash apparatus as defined in claim 1further comprisingcircuit means for disabling said control means fromproducing said alternating voltage only during the presence of a camerasignal.
 3. Electronic flash apparatus as defined in claim 1 furthercomprisingtiming circuit means for disabling said control means fromproducing said alternating voltage for a selected interval followinginitiation of said camera signal.
 4. Electronic flash apparatus asdefined in claim 1 for use with a camera having a battery and furthercomprisinga flash battery separate from the camera battery and forpowering the charging means, and an input stage of said control meanswhich receives said camera signal, said input stage being powered fromthe camera battery by means of said camera signal.
 5. Electronic flashapparatus for use with a camera of the type having a variable focusobjective lens and having sonic ranging and focusing means for theautomatic focusing of the objective lens, electrically-energizablecamera control means responsive to manual actuation for automaticallyoperating the ranging means for driving the objective lens from aninitial at-rest position to a focus position with respect to the sceneto be photographed, and for automatically returning the objective lensto the initial at-rest position, an electrical connector together withmeans for providing at the connector at first signal commencing inresponse to the manual actuation of the energizable camera controlmeans, and a second signal commencing in response to the objective lensbeing automatically driven from its initial at-rest position andterminating in response to the objective lens being returned to theat-rest position, and a flash fire signal, wherein the camera rangingand focusing means is subject to malfunction by interference fromspurious electromagnetic radiation,said electronic flash apparatushavinga flash-discharge tube, an energy-storage capacitor, an electricalconnector complementary to the camera connector for releasableconnection therewith, means energizable by an applied supply voltage forproducing an alternating voltage and a direct voltage in responsethereto, and for charging the capacitor with the direct voltage to aselect level and for thereafter maintaining the capacitor voltage withinselect limits, means responsive to the flash fire signal for dischargingsaid capacitor through said discharge tube to produce an illuminatingflash of light, and further comprising control means responsive to thefirst signal to occur of said first and second signals from the camerafor disabling said charging means from charging said capacitor so as toterminate production of the alternating voltage, and correspondingly ofspurious electromagnetic radiation, during at least the operation of thecamera ranging and focusing means.
 6. Electronic flash apparatus for usewith a single-lens reflex camera of the type having a variable focusobjective lens through which the user frames a scene to be photographedand having sonic ranging and focusing means for the automatic focusingof the objective lens, electrically-energizable camera control meansresponsive to manual actuation for automatically operating the rangingmeans for driving the objective lens from an initial at-rest position toa focus position with respect to the scene to be photographed, and forautomatically returning the objective lens to the initial at-restposition, an electrical connector together with means for providing atthe connector a first signal commencing in response to the manualactuation of the energizable camera control means, and a second signalcommencing in response to the objective lens being automatically drivenfrom its initial at-rest position and terminating in response to theobjective lens being returned to the at-rest position, and a flash firesignal, and wherein the camera ranging and focusing means is subject tomalfunction by interference from spurious electromagnetic radiation,saidelectronic flash apparatus havinga flash-discharge tube, anenergy-storage capacitor, an electrical connector complementary to thecamera connector for releasable connection therewith, means energizableby an applied supply voltage for producing an alternating voltage and adirect voltage in response thereto, and for charging the capacitor withthe direct voltage to a select level and for thereafter maintaining thecapacitor voltage within select limits, means responsive to the flashfire signal for discharging said capacitor through said discharge tubeto produce an illuminating flash of light, and further comprisingcontrol means responsive to the first signal to occurof said first andsecond signals from the camera for disabling said charging means for aselected time only from charging said capacitor so as to terminateproduction of the alternating voltage, and correspondingly of spuriouselectromagnetic radiation, during at least the operation of the cameraranging and focusing means, said control means thereafter enabling saidcharging means to again charge said capacitor for the interval betweentermination of said selected time and the last signal to occur of saidfirst and second signals. .Iadd.
 7. Electronic flash apparatus for usewith a camera of the type having automatic ranging means,electrically-energizable camera control means responsive to manualactuation for automatically operating the ranging means, and means forproviding a camera signal commencing in response to the manual actuationof the control means, and wherein the camera ranging means is subject todetrimental interference from spurious electromagnetic radiation,saidelectronic flash apparatus havingan energy-storage capacitor and aflash-discharge tube charging means energizable by an applied supplyvoltage for producing an alternating voltage and a direct voltage inresponse thereto, and for charging the capacitor with the directvoltage, means responsive to a flash fire signal from the camera fordischarging the capacitor through the flash tube, and further comprisingcontrol means responsive to said camera signal for disabling saidcharging means from producing said alternating voltage, so that theflash apparatus is disabled from producing spurious electromagneticradiation, during at least the operation of the camera ranging means..Iaddend. .Iadd.8. The apparatus of claim 7 wherein the automaticranging means ranges by way of a sonic signal. .Iaddend.